The present invention relates to a device of measuring a period of time during which blood coagulates, and more particularly, to a device of measuring a period of time required for a blood sample to coagulate, the device securing reproducibility and operational ease. Hereinafter, this period of time will be referred to as a blood coagulating time.
In general, there are many items under which ailments of animals as well as human beings are diagnosed by measuring a blood coagulating time; that is, a prothrombin time (PT), a partial thromboplastein time (PTT), a figrinogen quantity (Fbg), a deficient factor quantity, an activated partial thromboplastein time (APTT), and a Ca reapplication time. These items are decided on in accordance with the kind of a reagent to be added, and the part of the blood with which the reagent is caused to react. Take an example of a prothrombin time (PT), a systematic thromboplastein and calcium are adequately added to the plasma which was collected through centrifugal separation of blood. Subsequently, the period of time is measured until the production of whitish net-like fibrin lumps results. Let us take another example of the activated partial thromboplastein time (APTT). First, blood plasma is collected after the blood was subjected to centrifugal separation, and then acting is added thereto. In addition, calcium chloride is added. The period of time is measured until coagulation is formed More in detail, the blood plasma is stored in a refrigerator after it was obtained through centrifugal separation of blood. Acting of 0.1 ml, which was warmed in a water having a temperature of 37.degree. C. for a minute, is poured into a test tube containing 0.1 ml of the plasma The mixture is allowed to stay in a water of 37.degree. C. for two minutes. Then to this mixture, 0.1 ml of CaCl.sub.2 of 0.02 M, which had been placed in a water having a temperature of 37.degree. C., is added under pressure. At this moment a stop watch is switched on. The test tube is heated in the water of 37.degree. C. for 25 seconds. The test tube is taken out, and if coagulation is observed, the stop watch is turned off. In this way the blood coagulating time is measured.
The above described practice is a hand operated direct method, which is commonly called a manual method. This manual method requires a lot of skill and experience in carrying it out. Disadvantageously, it is difficult for inexperienced persons.
To overcome this difficulty of the manual method, an automatic measuring method has been proposed An optical method is a typical example, in which blood coagulations are optically detected However, under this method the coagulations are only locally detected, which is likely to result in an inaccurate measuring of a coagulating time In addition, the reproducibility is reduced. Furthermore, under the automatic methods it is a difficult problem how to define the blood coagulating time In an optical method a particular optical level is set, and when the level is crossed, it is accepted as the blood coagulating time being completed or when a point of change (the peak value obtained by differentiating the curve of changes with time) is observed, it is recognized as the blood coagulating time.
In the level detection it is likely to happen that the previously set level is not reached when the blood sample is abnormal. In such cases it is recorded as "measuring is impossible". Referring to FIGS. 1 and 2, the level L.sub.3 is set. FIG. 2 shows that the curve fails to reach the level L.sub.3, thereby causing the test to continue perpetually.
Referring to FIGS. 3 and 4, in which a point of change is to be detected, if the blood sample is abnormal, the detection will be difficult. It is likely that any change is mistaken as an expected point of change though it is actually not. This is shown in FIG. 4. The data obtained by the automatic methods of the above-mentioned kinds are not necessarily in accord with those obtained by the manual direct method, and for a diagnosis purpose it is necessary to adjust the measured values by comparison with those under the conventional method.